Accounts payable and accrued expenses (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Trade payables	$ 1,434,166	$ 1,175,023
Accrued compensation and benefits	833,141	227,323
Accrued professional fees	156,205	194,658
Accrued interest	750	86,100
Other payables	388,109	166,029
Total	$ 2,812,371	$ 1,849,133